Sen. Chuck Schumer’s plan for open primaries, issued in The New York Times this week, reminds me of how I became a Republican.

I’d been born and raised a Democrat and remained one until 2001, when I discovered that the candidate I wanted to vote for in the mayoral primary, Herman Badillo, was on the Republican ballot.

I switched my party registration, and I’ve never looked back (at least not with regret).

Schumer doesn’t want to go that route. Now that the Republicans may well win control of the Senate, he wants to change the primary system so that the GOP candidates can be selected by — wait for it — the Democrats.

That might sound like a joke. But Schumer endorsed this scheme in a Times oped piece headlined, “End Partisan Primaries, Save America.”

It seems that the Democrat boss has become seized of the notion that polarization and partisanship are a “plague on American politics.” The Senate, he writes, “hasn’t been so polarized since Reconstruction.”

Well, whose fault is that? It was Schumer who chaired the Democratic Senatorial Campaign Committee that set the strategy for delivering control of the upper house to the Democrats and the extremist Harry Reid and his camarilla.

It produced the very Senate that Schumer himself protests is so polarized. The Senate has refused so often to work with the Republican House that the Congress is, as he puts it, “on track to be among the least productive in our republic’s history.”

Schumer measures that productiveness by laws passed. For the long-suffering American taxpayer, the notion that Congress hasn’t passed as many laws as Schumer and his fellow Democrats want to pass is one of the few blessings in the age of Obama.

That idea might shock Schumer. In his book last year, “Positively American,” he described growing up thinking of government as “a benevolent patriarch watching over us, protecting us from a distance.”

Those were the days, weren’t they? Now Americans think of the government as a dangerous leviathan that is extracting from their wallets record tax receipts. Yet it’s still running up debts their grandchildren will have to pay.

Unemployment is still above 6 percent, even after millions have quit looking for work. Big corporations are moving overseas to escape our taxes, our southern border is in chaos and the military is being shrunk in a time of war.

The only hope this fall is that the GOP might gain control of the Senate and put through an economic-growth program. This would involve not only cutting taxes but deregulating business and restoring a sound dollar.

Schumer represents that he’s upset about what happened to Eric Cantor in Virginia: The House majority leader lost a primary that saw a late surge in voters.

Was he too liberal? Or did Virginia’s open primary enable Democrats to vote in the GOP contest and knock out a party superstar?

Why, when one stops to think about it, should members of one party be allowed to vote in another party’s primary? Can shareholders of General Motors — or persons with no shares at all — vote in the annual meeting for directors of Ford Motor Co.?

Schumer says he wants a “top-two” primary open to all with a run off. This seems to be a version of the scheme that Mayor Michael Bloom­berg tried to palm off on the noble electorate of New York. The mayor called it “nonpartisan” elections.

In November 2003 Bloomberg put it to the voters as a charter revision. Voters rejected it by an overwhelming majority of 70 percent. It was one of Bloomberg’s most stinging defeats.

What was he thinking? Voters aren’t dumb. They like political parties. Parties enable people of modest means to pool their resources and have an impact.

Does the ex-head of the Democratic Senatorial Campaign Committee actually want to sideline political parties running candidates? My guess is that he’s just maneuvering to avoid the coming Republican surge.

If Schumer thinks the Senate is too polarized, better for him just to be more compromising. Let him lead the effort to curb the political thuggery of Harry Reid.

And if he wants to vote in the Republican primaries, let him switch parties. I can tell him from experience, it’s liberating.